Current sensitive switches and electric irons embodying such switches



Dec. 13, 1955 w. M. RUSSELL 2,727,131

CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBODYING SUCH SWITCHESFilod Jan. 27, 1953 3 Sheets-Sheet l l5 2/ n 2o '1 1 I I 3/ 30 l L? O 2627 l 35 225 N ,6 29 22a 2" 24 28 w 25 I 22 23 36 O Q 37 FIE-Solo lnvemory Attorney W. M. RUSSELL CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONSEMBODYING SUCH SWITCHES Dec. 13, 1955 3 Sheets-Sheet 2 Filed Jan. 27,1953 FUE QO lnvenfor WWHM I Rose 8 w @604, Hwy Afl'rney /7 49 ZZSZW Dec.13, 19.55 -w. M. RUSSELL 2,727,131

CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBODYING SUCH SWITCHESFiled Jan. 27, 1955 I5 Sheets-Sheet 5 Inventor B W 6 ygwy' AfforneyUnited States Patent pun CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONSEMBQDYING SUCH SWITCHES William Morris Russell, Bromley, England,assignor to Morphy-Richards Limited, St. Mary Cray, England, a Britishcompany Application January 27, 15 53, Serial No. 333,469

11 Claims. (Cl. 21925) This invention relates to an electric switch forcontrolling an ancillary circuit in accordance with the value of thecurrent flowing in a main circuit.

Broadly, the invention lies in the provision of a switch for the purposestated, which comprises two members both responsive to the currentflowing in a main circuit, but having relatively slow and fast speeds ofresponse. The slow response member acts to cause eventually theoperation of switching means in the ancillary circuit unless the valueof the current in the main circuit bears a predetermined relationship toa critical value, in which case the fast response member acts to inhibitthe operation of said switching means. The arrangement can be such thata normally open ancillary circuit is completed by said switching means,the switching means operating only when the current in the main circuitis less than a critical value.

A switch in accordance with the invention has particular application inan electric smoothing iron of the type for use on electricity suppliesof diiferent voltages. This type of iron has two heater elements; a mainheater element which is energised whatever the supply voltage may be,and an ancillary heater element which is energised only when the supplyis of a voltage below a critical value. Although there are a fewexceptions, in general public supply voltages lie either in the range100 to 120 volts or in the range 200 to 250 volts. Thus, the criticalvalue can be taken as some value intermediate 120 and 209 volts and theheater elements can be chosen so that the two elements on the lowerrange of voltages give substantially the same sole-plate temperature asthe single main element on the higher range. If the iron is fitted witha thermostat this relationship will, of course, apply for each settingof the thermostat.

Thus, the invention also comprises an electric smoothing iron of thetype specified, which iron is provided with a switch as broadly definedabove, to effect automatically the inclusion of the ancillary heaterelement in the iron circuit it, but only if, the voltage of the supplyto which the iron is connected is below a critical value.

In accordance with the invention there can be provided an electricsmoothing iron having a normally closed main circuit which includes amain heater element, a normally open ancillary circuit in shunt to themain circuit and including an ancillary heater element, and a switchresponsive to the flow or" current in the main circuit and adapted toclose the ancillary circuit if, but only if, that current is below agiven critical value.

In order that the invention may be more fully and clearly understood,there will now be described with reference to the accompanying drawings,an electric switch constructed in accordance with the invention for usein effecting the automatic switching of the ancillary heater element inan electric iron of the type specified.

In the drawings:

Figure 1 is a plan view of the sole plate of an electric smoothing ironfitted with a main and ancillary heater element, a thermostat and aswitch in accordance with 2,727,131 Patented Dec. 13, 1955 the presentinvention, and the parts of said switch being shown in a somewhatsimplified manner;

Figure 2 is a plan View of the switch of Figure 1, on an enlarged scale,and shown in greater detail;

Figure 3 is an end view of the switch from above in Figure 2;

Figure 4 is a side view of the switch from the right in Figure 2;

Figure 5 is a side view of the switch from the left in Figure 2; and

Figure 6 is a sectional side view of the switch taken on the line VIVIof Figure 2.

There is shown in Figure l, a sole plate 10 of a smoothing iron having amain and ancillary heater element for the purpose previously mentioned.The two heater elements are held against the sole plate 14) by means oftwo clamping members 11 (the elements being hidden thereby in the viewof Figure 1); the manner of thus securing the heater elements forms nopart of the present invention, and is fully described in the completespecification of my copending application S. N. 314,442 now Patent No.2,701,293. Mounted on the sole plate ltl are a thermostat 12 and aswitch 13 constructed in accordance with the invention. The thermostatincludes a temperature responsive device such as a bimetal strip whichoperates contacts to open and close the iron circuit in such a way astends to maintain the sole plate temperature at the thermostat setting.The construction of such thermo stats is well known and will not bedescribed herein beyond the statement that the two terminals of thethermostat are provided by a screw 14 and metal strip 15.

Before describing in detail the construction of the switch 13, theelectrical arrangements of the switch and the iron in which it isincorporated will be explained with reference to Figure 1.

The switch components are mounted on a base 16 of insulating materialand include three metal plates 17, 18 and 19 which as well as providingthe main mechanical support for the moving parts of the switch functionas electrical connectors. A lever 20 is pivotally supported on the base16 and is electrically connected to plate 17. To the short arm of thislever, one end of a hot wire 21 is attached; the other end of the hotwire is supported by but insulated from plate 17 and is electricallyconnected to one lead 22a of a heater coil 22. The heater coil is woundon and serves to heat a bimetal strip 23 and its other lead 22b isconnected to plate 18. The left end (in Figure 1) of the bimetal isfixed, and a contact or operating lever 24 is held against the other endby a spring strip 25 secured to plate 17. Contact 26 carried by lever 24is connected electrically to plate 17 via lever 24 and spring strip 25.Contact 26 cooperates with a fixed contact 27 which is in electricalcommunication with plate 19; this pair of contacts efiect the completionof the ancillary circuit when required. Strip 25 carries a contact 28which co-operates with a fixed contact 29 on plate 18. Plate 18 alsocarries contact 30 co-operating with contact 31 on the longer arm of thelever 20.

Two terminals 32 and 33 insulatingly mounted on sole plate 10 areadapted to be connected to an electricity supply in any suitable manner.When the iron is initially connected to the supply, the iron circuit isas follows: from terminal 33 through wire 34 to terminal 14 ofthermostat 12, terminal 15 of the thermostat to plate 17 of switch 13,lever 20, hot wire 21, bimetal heater coil 22, plate 18, conductingstrip 35 which is connected to one end of the main heater element. Theother end of this element is connected by conducting strip 36 toterminal 32 thereby completing the circuit so that the main heaterelement is energised. One end of the ancillary heater element is alsoconnected to strip 36, the other end however is connected by strip 37 toplate 19 and hence initially the ancillary element is not in circuit.

The mechanical arrangements (to be described later) of switch 13 and therelative speeds of response of hot wire 21 and bimetal strip 22 to theheating effect of the current are such that contacts 26 and 27 willclose if, but only if, the current is below a critical value. Thiscritical value corresponds to a critical voltage value below which it isnecessary that the ancillary heater element is energised. Closure ofcontacts 26 and 27 effect the connection of the ancillary element in theiron circuit by completing a circuit from plate 17 through the ancillaryelement to connect it in parallel with the main element. This circuit isas follows: plate 17, spring strip 25, contact lever 24, contact 26,contact 27,'plate 19, strip 37, the ancillary heater element and strip36.

If the supply voltage is greater than the aforesaid critical'value thencontacts 26 and 27 do not close and the ancillary heater element remainsout of circuit. When the switch 13 has operated, whether to connect theancillary element or not, contacts 28 and 29 close thereby connectingplate 17 to plate 18 via strips 25 and said contacts. This connectionshort circuits the hot wire 21 and bimetal heater 22 which remainshort-circuited as long as the iron is hot.

The construction and mechanical operation of the switch 13 will now bedescribed in greater detail with reference to Figures 2 to 6. The threemetal plates 17, 18 and 19 are fastened to the insulating base 16 bymeans of eyelets such as 38. A U-bracket 39 has a longer limb which islocated in a recess in the base 16 and is secured between the base andplate 17. A pin 40 is supported between the limbs of bracket 39; thelever 20 is pivotally secured on this pin by bending two marginalportions of the lever around the pin, the central portion thus leftforming the shorter armof the lever. Electrical connection of the lever20 to plate 17 is ensured by a flexible, conductive strip 41 spot weldedto lever 20 and to a flange 17bo n plate 17. i

The hot wire 21 consists of a nickel-chrome tape, one endof which issecured to the shorter arm of lever 20; the tape then passes through alongitudinal slot in the other arm of the lever. The means forsecuringthe other end of the tape are adjustable to enable the initial positionof the lever 20 to be varied and comprises a flanged plate 42. Thisplate has a L-shaped flange 42a (see Figure 4) by means of which itissupported some distance above plate 17 ona pivot pin 43. Another flange42b. held against an adjustable stop 44. by means of a spring 45. To athird flange 420 of plate 42, an angle bracket 46 is fastened by meansof an eyelet 47; bracket 46 and eyelet 47 are electrically insulatedfrom plate 42- hy means of two insulating washers 48. The end of thehotwire 2 1 is threaded through the eyelet 47 and through holes inbracket 46 to which it, is then spot welded; Also spot welded to thebracket is one lead 22a of the bimetal heater coil 22. This lead passesthrough an insulating sleeve 49., the coil proper being wound about thebimetal strip 23 from which it is insulated by two thin mica strips 50.The other lead 22b of the coil 22 is accommodated in'a groove in theunderside of the base 16 and passes through a hole in the base to bespot welded to the plate 18. i

' The bimetal strip 23 is secured at one end to a flange 175 on plate17. It is required that contact or operating lever 24 should be able topivot about a first fulcrum provided by the end of the longer arm oflever'20 or about a second fixed fulcrum provided by the flange 170. Thelever 24 is therefore not secured to any other part of the switch 13 butis held in the required position by means of the spring strip 25 whichis secured at one end to the flange 17c. The other end of the spring25"is hooked around the free end of the bimetal strip "23 so as to holdit against the curved end of'the contact lever 24; The other end of thecontact lever is bent so as to engage the flange 17c, whilstintermediate its ends the lever has a stop 24a bent-out of the lever.This stop passes through a slot in strip 25 and is adapted to engage theend of lever 20.

As previously explained, when the iron is connected to a supply, currentwill flow through hot wire 21 and bimetal heater 22. Thus, thetemperature of the hot wire will increase and consequently its lengthwill increase thereby permitting lever 20 to be turned in ananti-clockwise direction by spring 51. It will be noted that themovement of hot wire 21 is magnified by the arrangement of lever 20. Atthe same time, the temperature of bimetal strip 23 increases, this stripbeing arranged so that its free end moves in a direction towards the topof Figure 2 with increase in temperature. The curved end of contactlever 24 moves with the bimetal and initially the contact lever pivotsabout flange 17c.

it is arranged that if the supply voltage is above the critical voltagepreviously referred to, the speed of response of the hot wire relativeto the bimetal strip is such that the end of lever '20 has moved clearof "stop 240 before it can be engaged thereby. Lever 24 will thereforecontinue to pivot about flange 17c so that contacts 26 and 27 are notclosed and the ancillary heater element remains out of circuit. In duecourse the movement of lever 24 will bring contact 28 into engagementwith fixed contact 29 thereby short-circuiting the hot wire and bimetalheater as explained above.

If the voltage supplied to the iron is below the critical value, i. e.it is such that both heater elements must be energised to give therequired temperature, then the relative movements of levers 20 and 24produced are such that stop 24a engages the end of lever 20. Thereafter,lever 24 pivots about the end of lever 20 in an anti-clockwise directionso that contact 26 moves towards contact 27. Eventually contacts 26 and27 will close thereby completing the ancillary heater element circuit asis required. As before, the bimetal will continue to move until thecontacts 28 and 29 close. It should be noted that contact 27 is carriedby a flexible strip 52 secured to a flange 19a on plate 19. In this way,contact 27 is permitted to move with contact 26 after they'have closedand before contacts 28 and 29 close.

Contact 29 is in the form of a screw in a flange 18a on plate 18, towhich flange it is locked by means of a nut 53. This arrangement permitsthe position of contact 29 tobe pre-set' so that contacts 28 and 29close at the optimum time. Flange also carries contact 30 whichco-operates with contact 31. This pair of contacts are in parallel withcontacts 28 and 29 and act as a safety means to prevent damage to theswitch 13 should the voltage be so great as to cause lever 20 to movesharply over, contacts 30 and 31 then closing in advance of contacts 28and 29 and serving the same purpose.

In order to prevent repeated operations of the, switch after it has onceoperated to effect control of the aricillary heater circuit, it isarranged that as long as the iron remains at the temperatures normallyused, the heat from the sole plate is suflicient to maintain the bimetalstrip in a position in which the short-circuiting contacts 2 8 and 29are closed.

While the switch construction described above is at. present thepreferred embodiment of the invention, modified constructions for use ina smoothing iron or for other uses can be adopted without departing fromthe scope of: the invention. For example, a bimetal strip can beemployed for both the slow and the fast current responsive members. Theslow response bimetal is heated by conduction from a member on which aheater coil is wound while the fast response bimetal is selfheated, thatis it is heated by flow of current through the strip itself, which islongitudinally slotted to provide a narrow current path of'zig-zag'form.

1 claim:

1. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising a base, switch contacts for inclusion in the ancillarycircuit, operating means for said switch contacts and first and secondcurrent responsive members mounted on said base which move in responseto thecurrent flowing in the main circuit, said second member having afaster speed of response than said first member, said first and secondcurrent responsive members being constructed and arranged so that themovement of one of said members causes actuation of said operating meanswhen the current in the main circuit diifers in one sense from apredetermined critical value and the movement of the other of saidmembers prevents such actuation when said current difiers in theopposite sense from said critical value.

2. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising a base, normally open contacts for inclusion in the ancillarycircuit, contact operating means adapted to close said contacts whenactuated, and first and second current responsive members mounted onsaid base which move in response to the current flowing in the maincircuit, said second member having a greater rate of displacement thansaid first member, said first and second current responsive membersbeing constructed and arranged so that when the current in the maincircuit is less than a predetermined critical value the displacement ofsaid first member actuates said contact operating means and when thecurrent in the main circuit is greater than said predetermined criticalvalue, the displacement of said second member modifies the displacementof said first member and thereby prevents it from actuating said contactoperating means.

3. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising a base, circuit switching means for inclusion in theancillary circuit, operating means adapted to operate said circuitswitching means when actuated, and first and second temperaturesensitive members mounted on said base, each of which moves in responseto heat produced by the current flowing in the main circuit to produce adisplace ment of the member at a rate dependent on the value of saidcurrent, the displacement of said second temperature sensitive memberoccurring for any value of current at a greater rate than that of saidfirst member, the first and second temperature sensitive members beingconstructed and arranged so that when said current differs in one sensefrom a predetermined critical value, the displacement of said firstmember is such as to cause actuation of said operating means and whensaid current differs in the opposite sense from said critical value, thedisplacement of said second member prevents displacement of said firstmember from causing actuation of said operating means.

4. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising a base, normally open contacts for inclusion in the ancillarycircuit, con tact operating means adapted to close said contacts whenactuated, and first and second temperature sensitive members mounted onsaid base each of which is so positioned with respect to said maincircuit as to be heated when current flows therethrough and adapted tobe displaced in response to heat produced by said current, the rate ofdisplacement ofsaid second member being greater for a given value ofsaid current than that of said first member, said first and secondtemperature sensitive members being constructed and arranged so thatwhen said current is less than a predetermined critical value thedisplacement of said first member is such as to produce actuation ofsaid contact operating means and when said 6 current is greater thansaid critical value, the displacement of said second member is such thatthe displacement of said first member is modified thereby to prevent itsactuation of said contact operating means.

5. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising normally open contacts for inclusion in the ancillarycircuit, an electric heating coil in the main circuit, a bimetal stripin heat exchange relationship with said heating coil, a hot wire in themain circuit, the length of which hot wire increases when itstemperature is raised by current flowing therethrough, andcontact-operating means for operating said contacts, saidcontact-operating means being under the joint control of said bimetalstrip and said hot wire, the arrangement being such that when thecurrent in the main circuit is less than a predetermined critical valuesaid contacts are closed and when said current is greater than saidcritical value said contacts remain open.

6. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising normally open contacts for inclusion in the ancillarycircuit, an electric heating coil in the main circuit, a bimetal stripin heat exchange relationship with said heating coil, a hot wire also inthe main circuit the length of which hot wire increases when itstemperature is raised by current flowing therethrough, a swingable leverwhich controls the position of one of said contacts and is coupled tosaid bimetal strip, a first fulcrum normally adjacent said lever, theexact position of which fulcrum is controlled by said hot wire, and asecond fixed fulcrum adjacent said lever, whereby bending of saidbimetal strip due to an increase in the temperature thereof causes saidlever to pivot about said first fulcrum to close said contacts when saidcurrent is less than a predetermined critical value but to pivot aboutsaid second fulcrum without closing said contacts when said current isgreater than said predetermined critical value, said first fulcrum beingwithdrawn from its position adjacent said lever as the result of theincrease in length of said hot wire in response to said greater current.

7. An electric switch as claimed in claim 6 in which said heating coiland said hot wire are connected in series and comprising furthernormally open contacts connected in parallel with said series-connectedheating coil and hot wire, said lever being arranged so as to eventuallyclose said further contacts after pivoting about said first or secondfulcrum.

8. An electric switch for controlling an ancillary circuit in accordancewith the value of the current flowing in a main circuit, said switchcomprising a base, first normally open contacts for inclusion in theancillary circuit, a bimetal strip having one end attached to said basean electric heating coil adapted to heat said bimetal strip, a hot wirethe length of which increases substantially when current flowstherethrough, said heating coil and said hot wire being connected inseries for inclusion in the main circuit, a first lever pivotallymounted on said base and having a short arm and a long arm with a firstfulcrum in the free end thereof said hot wire having one end attached tosaid base and the other end to said short arm of said first lever, aspring attached between said long arm of said first lever and said baseand arranged to maintain said hot wire under tension, a second fulcrumfixed to said base, a second lever mounted so as to be capable ofpivoting about said first or second fulcrum, means coupling said secondlever to said bimetal strip whereby bending of said bimetal strip due tothe heating thereof effects pivotal movement of said second lever,second normally open contacts connected in parallel with saidseriesconnected heating coil and hot wire, the arrangement being suchthat when the current in the main circuit is less than a predeterminedcritical value said second lever is pivoted about said first fulcrum toclose said first con- 7 tactsand .thereafiter closes said secondcontacts and when ai u rents r ate tha ai c tical val v ai se ver is pvptd a sut a d se n t lc um nd clos s on y said second contacts.

9. An electric switch as claimed in claim 8 comprising third normallyopen contacts connected in parallel with sai d second contacts andadapted to be closed by said first lever if the movement thereof isexcessive.

it). An electric smoothing iron for use on electricity supplies ofdifferent voltages comprising a main heater element. for connection tothe supply whatever its voltage and an ancillary heater element forconnection to. the supply only when the voltage thereof is less than apredetermined critical value and a switch for automatically efiecting.such connection of the ancillary element, said switch. comprising abase, normally open contacts conlfiQted in series with the ancillaryheater element and adaptedv to be connected. in series with the supplythe supply, contact-operatingmeans onsaid base adapted to close said.contacts when actuated, and first and second temperature-sensitivemembers onsaid. base each of which is displaced in response to heatproduced by the current flowing in the main heater element, the rate ofdisplacement of said second member being greater for a given value ofsaid current than. that of said first member, said first and secondtemperature sensitive members being constructed and arranged so thatwhen said current is less than a. predetermined. critical value, whichcorresponds to said critical voltage value, the displacement of: saidfirst member is such as to produce actuation of said contact. operatingmeans and when said current is greater than said critical value, thedisplacement of said second member is such as to prevent thedisplacement of idv first m m r n m a ins a tuat on of sai sontaoperating means.

11. An electric smoothing iron for. use on electricity upn o diff re t vt c m r s n a a n hea er element adapted to be connected to-the supplywhatever its voltage and: an ancillary heater elementv connected. inparallel with said. main heater element only when the supply is of avoltage less than a predetermined. critical value, and a switchcomprising a base, normally open contacts in series with the ancillaryelement, a bime al strip carried on said base. heated by thecurrentflowing in the main element, afirst member actuated by the movement ofsaid bimetal strip when it is; heated. to cause closure. of saidcontacts unless the supply voltage is greater: than said critical value,a hot wire also heated by the current flowing in the mainelement, and asecond member. ac: tuated by movement of thehot wire when it. is heated,the displacement of said secondtrnember when the supply voltage isgreater than: said critical value being. such as to modify thedisplacement of said first member. so as.

to prevent its closing said 'contacts.

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